The present disclosure provides methods and materials for the diagnosis and screening of liver pathologies, including proliferative or degenerative diseases of the liver; and more particularly, methods and materials for the quantification or determination of progastrin levels to diagnose liver pathologies.
3.1. Background of the Gastrin and Progastrin Hormones
Gastrin is a gut peptide hormone that functions as a stimulant of gastric acid secretion. In the adult mammal, it is produced principally by the G cells of the gastric antrum and to a variable extent in the upper small intestine and pancreas, with barely detectable amounts in the colon. Recently, there has been increasing interest in the role of the gastrin family of peptides in colorectal carcinogenesis. In particular, there is evidence that the precursor forms of gastrin (progastrin and glycine-extended gastrin), which were previously thought to be inactive, play a role in the development of colorectal cancer.
The gastrin gene is translated into a 101-amino acid polypeptide, called preprogastrin, which contains a signal sequence (underlined) that is cleaved, giving rise to progastrin, an 80-amino acid polypeptide. In turn, progastrin is processed to provide the cleavage product G34, a 34-amino acid peptide corresponding to residues 38 to 71 of progastrin. G34 is then extended at its carboxy terminus with a glycine residue, generating glycine-extended G34 (G34-Gly). A by-product of progastrin cleavage is a 6-amino acid peptide, called the C-terminal flanking peptide, or CTFP, which corresponds in sequence to residues 75 to 80 of progastrin. G34-Gly is then further cleaved to generate a 18-residue polypeptide corresponding in sequence to residues 55 to 72 of progastrin and referred to as G17-Gly. Removal of the C-terminal glycines of G34-Gly and G17-Gly, followed by C-terminal amidation, yields G34 and G17, respectively, both of which are C-terminally amidated.
Most assays for progastrin do not distinguish between progastrin and other gastrin gene products, resulting in an inaccurate measurement of full-length progastrin levels. Because progastrin levels play a role in one or more diseases, accurate means for the measurement of progastrin are desirable.
3.2. Background of Liver Pathologies
Many liver pathologies are difficult to diagnose. For example, liver cancer cannot be diagnosed by routine blood tests. Physician screening with the tumor marker alpha-fetoprotein (AFP) is usually necessary. However, elevated AFP levels are not specific for liver cancer. In adults, high blood levels (over 500 ng/mL) of AFP are seen in three situations: liver cancer, germ cell tumors (cancers of the testes and ovaries), and metastatic cancer of the liver (a cancer originating in other organs). In addition, the sensitivity of AFP for liver cancer is about 60%. In other words, an elevated AFP blood level is seen in only about 60% of liver cancer patients; 40% of patients with liver cancer have normal AFP levels. Another difficult to diagnose liver pathology is cirrhosis, a consequence of chronic liver disease characterized by scarring of the liver and poor liver function. The gold standard of diagnosis is by way of liver biopsy, an invasive technique.
Hepatitis C is an infectious disease affecting the liver, caused by the hepatitis C virus (HCV). The infection is often asymptomatic, but once established, chronic infection can progress to scarring of the liver (fibrosis) and advanced scarring (cirrhosis). Hepatitis C is typically diagnosed by way of serological screening. Other means for detecting and/or confirming hepatitis C would be desirable.
Because the early and accurate detection of liver cancer, cirrhosis, and hepatitis C has the potential to increase the survival rate of a patient, there is a present and long-felt need for methods of diagnosing or detecting these pathologies, including instances where a patient has more than one or all of the aforementioned diseases.